1. Field of the Invention
The present invention relates to a method of preparation for a biodegradable co-polyester with divided addition of an aromatic dicarboxylic acid compound, and more particularly, to a method of preparation for a biodegradable co-polyester in which an aliphatic dihydroxy compound and an aliphatic dicarboxylic acid compound are first esterificated to improve a solubility and reactivity of an aromatic dicarboxylic acid compound which is a reactant for a process of preparation for a biodegradable co-polyester, and then the aromatic dicarboxylic acid compound is dividedly added thereto, thereby increasing the solubility of the aromatic dicarboxylic acid compound and reducing a side reaction.
2. Discussion of Related Art
A biodegradable resin is a synthetic resin developed as a new material which is degraded into water and carbon dioxide or water by a microorganism, such as bacteria, algae, and fungi, existent in nature and does not cause environmental contamination.
The biodegradable resin widely used together with cellulose-based polymers and starches is a resin produced from aliphatic polyester such as polylactic acid (PLA), polybutylene succinate (PBS), polyethylene succinate (PES), and polycaprolactone (PCL).
Such an aliphatic polyester resin has a high biodegradability, but there is a disadvantage in that it has a low mechanical property. Therefore, in order to complement mechanical strength of the aliphatic polyester resin, there has been developed a method of preparing a biodegradable resin in the form of an aliphatic-aromatic copolymer through synthesis by adding an aromatic monomer to a process of producing a biodegradable resin.
At this time, as an aromatic monomer, dimethyl terephthalate (DMT) has been typically used. There is an advantage in that since the dimethyl terephthalate can react even at a reaction temperature of 200° C. or less, a reaction can be easily induced. However, there is a disadvantage in that the dimethyl terephthalate is expensive, thereby increasing cost burden.
Thus, there have been made continuous efforts to prepare a copolymer by using an aromatic monomer cheaper than the dimethyl terephthalate. By way of representative example, there has been suggested a method of using terephthalic acid (PTA) as aromatic dicarboxylic acid for a synthesis reaction of a copolymer.
However, unlike dimethyl terephthalate, terephthalic acid has no melting point and sublimates at a high temperature. Further, terephthalic acid is slightly dissolved in 1,4-butanediol (BDO), which is used as a representative aliphatic monomer for a process of preparing a biodegradable polyester resin, under normal pressure only at a temperature of 220° C. or more. Therefore, a reaction temperature of 220° C. or more is required to induce a uniform reaction between terephthalic acid and 1,4-butanediol. However, 1,4-butanediol is easily converted into tetrahydrofuran (THF) at a temperature of 200° C. under acidic conditions. Therefore, in a process of preparing a copolymer using an aromatic monomer such as terephthalic acid requiring a high reaction temperature and acidic reaction conditions, an excessive amount of an aliphatic monomer such as 1,4-butanediol needs to be used in consideration of an amount of the aliphatic monomer converted into tetrahydrofuran. In order to prevent waste of such an aliphatic dihydroxy compound, the aliphatic dihydroxy compound is allowed to react first with an aliphatic dicarboxylic acid compound having a relatively low acidity.
Poly(butylene adipate-co-terephthalate) (PBAT) is a representative biodegradable resin in the form of an aliphatic-aromatic copolymer prepared using terephthalic acid as an aromatic monomer and 1,4-butanediol and adipic acid as aliphatic monomers as described above.
However, as for PBAT, as depicted in FIG. 1, if an aromatic monomer such as terephthalic acid is directly added to a reaction of 1,4-butanediol and adipic acid, terephthalic acid is not completely dissolved due to its low solubility and a competitive reaction between an esterification reaction (1) and a cyclization reaction as a side reaction (for example, conversion (4) of 1,4-butanediol into THF) continues until the esterification reaction completes. Therefore, there is a disadvantage in that the esterification reaction is delayed and the side reaction is accelerated.
Accordingly, the present inventors have found that in a process of preparation for a biodegradable co-polyester, if an aliphatic dihydroxy compound and an aliphatic dicarboxylic acid compound are first esterificated and then an aromatic dicarboxylic acid compound is dividedly added thereto, a solubility of the aromatic dicarboxylic acid compound can be increased so as to reduce a side reaction without a delay in an esterification reaction and thus, completed the present invention.